Breastfeeding is essential for optimal growth and survival of infants, especially in developing countries. However, some infants appear to have acquired HIV from their mothers via breastfeeding. our preliminary data indicate that the majority of seropositive women have HIV DNA in their breast milk, but most breastfed infants born to HIV seropositive women do not become infected. We propose to expand our current studies in order to determine the prevalence and pattern of HIV in breast milk, to identify maternal factors associated with HIV in breast milk and to evaluate anti-HIV factors in breast milk and in infant's saliva that might protect against maternal-infant transmission via this route. Four hundred and twenty five HIV seropositive women, 260 seronegative women and their infants will be followed for 18 months. Serial breast milk, blood and saliva specimens will be collected and evaluated after the HIV infection status of the infant has been determined. Breast milk specimens from all women who transmitted infection to their infants will be compared to breast milk from mothers of uninfected infants. The breast milk specimens will be cultured for HIV, evaluated by PCR for HIV DNA and RNA and assayed for evidence of anti-HIV activity. The presence of HIV in breast milk will be correlated with maternal clinical and immunologic status and with maternal-infant HIV transmission. Lastly, saliva specimens collected in early infancy from infected and uninfected infants will be evaluated for HIV inhibitory activity. These studies will provide valuable information regarding the role of breast milk in maternal-infant transmission of HIV.